You want to virtualize three guests running application XYZ on Red Hat Enterprise Linux. Red Hat Enterprise Linux 5 requires 5GB of disk space and application XYZ requires 2GB of disk space. Red Hat Enterprise Linux requires a minimum of 512MB of RAM application XYZ requires up to 256MB of RAM. Application XYZ runs best on just one processing core.
The minimum system requirements for a system running application XYZ on three Red Hat Enterprise Linux guests are:
21GB of free disk space available to the host,
2304MB(768GB x 3) + 1024MB(for the host) = approximately 3.5GB of RAM, and
3 processing cores + 1 for the host(for better performance).